Show warnings if JS is disabled or when the detected browser version is outdated

* The Echo3 server-side implementation now adds a noscript-element
  with a warning that shows up when JavaScript is disabled in the user's browser.
  The text and link displayed can be customized in ServerConfiguration.

* A warning is shown at client startup when the detected browser version is considered outdated
  by the current Echo3 client-side implementation (detected in Echo.Client._isBrowserOutdated).
  The text of the default warning implementation Echo.Client.DefaultOutdatedBrowserWarning
  can be configured using new 'ClientConfiguration' properties or substituted
  by a new implementation analogous to WaitIndicator. An example implementation is included in
  the interactive test application. The warning can be disabled by setting the
  ClientConfiguration.OUTDATED_BROWSER_NO_WARNING flag.

Resolves #59